Transmitters are used in a variety of industries and their uses differ widely. However, one particular implementation is a transmitter in communication with a measuring instrument, such as a fluid flow meter. Typically, the fluid flow meter is connected inline in a pipeline or the like and therefore is generally located remote from a central control station or other processing system. The transmitter may receive signals from the flow meter and transmit the signals to a control system or the like for further processing.
In certain situations, a vast amount of information may be transmitted to the control system without a user/operator actually examining the information. There may be significant gaps in time before the data transmitted to the control system is examined. In some situations, the data may not be examined unless there is a detected problem in the flow. Once a problem is detected, the operator may have to review the data and correlate that data to an event that occurred at a specific time. Therefore, transmitters are typically equipped with a real-time clock so that each piece of data sent to the control system can be timestamped for later review.
The use of a real-time clock certainly has advantages in that the clock can accurately monitor when certain events occur. The event may relate to certain flow conditions, for example. One problem with the use of a real-time clock is that in order to maintain an accurate time, the clock must be provided with power even during times when the transmitter is not being used, i.e., the transmitter is not powered. Therefore, prior art transmitters having real-time clocks have required a battery backup to power the clock during periods of non-use. The use of battery backups may not be practical for a number of reasons, including cost and space considerations. The alternative to having a battery is to constantly provide power to the transmitter even during periods when the transmitter is not transmitting information to the control system. This solution may not be practical for various other reasons. For example, if the flow meter is operating under a power constraint, the additional power required to operate the real-time clock may not be available during all times. Furthermore, during extended periods between uses, continuously supplying power may not be justified. If the real-time clock temporarily lost power, the transmitter could send data having an incorrect timestamp. The error may not be discovered for an extended period of time. The incorrect timestamp may prevent a user/operator from diagnosing a problem in the flow meter, for example. Therefore, an accurate timestamp can provide significant information to the user/operator.
Therefore, there exists a need in the art to provide a process control system that can accurately assign a real-time timestamp to measurements without the drawbacks associated with providing the transmitter a real-time clock. The present invention solves this and other problems and an advance in the art is achieved.